In 1985, Paul Hepler, captain of the charter boat Venture III, made one such discovery. While he was mapping the ocean bottom with a magnometer, he found two extremely rare locomotive trains on the ocean floor–mysteriously sitting perfectly upright, with no part sunken into the ground beneath it. Found only 90 feet underwater, about 5 miles off the coast of New Jersey, Hepler–and countless researchers–were mystified at their unusual discovery.

Even after more than 20 dives and countless hours of research, no one knows for sure how or why the trains ended up at the bottom of the Atlantic. Some popular theories are that the locomotives were cast off of a ship purposefully or fell off a ship during a strong storm, possibly during a journey being from a factory in Boston to a port in the Mid-Atlantic states. While the details of how the trains arrived at their final resting place, there are a few facts about them that can be confirmed.

After more research, it was discovered that the trains were from the 1850’s and were “rare Planet Class 2-2-2 T models, which were only made for a short time because they became obsolete nearly as soon as they were produced,” according to a DailyMail article. To put their sizes into perspective, the article further describes the trains: “They were fully-loaded, self contained 15-ton locomotives at a time when steam engines were being produced at 35 tons.”

But that’s not all. These were also two of the oldest remaining steam locomotives ever built in the United States; only a handful still exist. Undersized, extremely rare and representative of only a tiny window in history; to say these trains were an unexpected find is an understatement.

While the initial discovery was made three decades ago, it was only in 2013 that these findings were made public. See up-close-and-personal footage of the trains in the video below.